sedimentary

Borehole Rock / Pierced Stone

Sedimentary rock with naturally eroded piddock clam boring (Hag Stone)

Hardness varies from 3 to 7 depending on host rock; tan to grey color; dull luster; amorphous structure formed by erosion.

Identified November 7, 2026More sedimentary →

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Physical properties

Hardness varies from 3 to 7 depending on host rock; tan to grey color; dull luster; amorphous structure formed by erosion.

Formed through mechanical and biological weathering, often by marine organisms drilling into sedimentary rock formations over thousands of years.

Commonly collected as curiosities, used in folk traditions, or displayed as unique natural geological specimens.

Historically known as hag stones or witch stones, folkloric tradition held they could ward off negative energy or allow sight into the spirit realm.

Easily identified by naturally occurring holes or grooves drilled completely through the rock by marine bivalves; found on beaches and riverbanks.

Fossil-bearing concretion, possibly containing a fossil shell or other organic inclusion

Calcareous concretion; exact fossil and host-rock composition are not identifiable from the image

Fossiliferous Sedimentary Rock

Sedimentary limestone with invertebrate fossil imprint

Sandstone or Siltstone

Arenite (if sandstone)

Sandstone

Arenite

Shale

Shale (clastic sedimentary rock)

Shale (or Mudstone/Siltstone)

Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)